This application relates to the fixing of a toner powder image on a sheet of material. It has particular application to the fixing of a toner powder image which has been produced by an electrostatic photocopying process.
In an electrostatic photocopying process an image is produced on a sheet of material by the adhesion of toner powder particles to a sheet of material by electrostatic forces. In certain types of electrostatic photocopying processes the image is developed by adhesion of toner particles to a sheet of material which has been treated with a photoconductive material such as zinc oxide and the sheet of material forms the actual copy sheet. In another known form of photocopying process a developed image is subsequently transferred to a sheet of plain paper with the toner powder image initially adhered to the sheet of paper by electrostatic forces.
In the use of either type of photocopying process it is necessary to fix the toner powder image to the sheet of material. Otherwise, the electrostatic forces would not be sufficient to maintain the image on the sheet of material for any appreciable length of time. Heretofore, the conventional ways of fixing the toner powder image on the sheet of material have been by application of heat, pressure or a combination of heat and pressure. The conventional manner of applying pressure has been to pass the sheet of material through a nip formed by a pair of pressure rollers.